Perforation systems for perforating various types of sheet material have been utilized in a variety of fields. One particular field in which systems of this type have been used is the field of cigarette manufacture. In cigarette manufacture, perforating systems are employed to perforate cigarette rod paper and/or cigarette filter tipping paper to provide cigarettes having preselected dilution characteristics. Perforation systems for this purpose must be capable of providing precise and uniform perforation patterns or matrices to achieve with consistency the desired dilution characteristics.
To date mechanical puncture systems and electric arc systems have been developed for cigarette paper perforation. With these systems, individual perforating elements provide perforations for a particular row of a perforation pattern and uniformity of the pattern is ensured by synchronizing operation of the perforating elements. Another type of system for perforating cigarette paper involves the use of laser beams. Systems of this type have employed single or multiple laser beam sources and controlled movement of these sources and the paper to realize perforation patterns having the desired precision. Laser beam practices have also been proposed wherein beam splitting optical components provide a multiple of component beams which are focussed on the paper to provide multiple perforations.
Another laser beam perforating practice is also known wherein multiple perforations are realized by confronting the laser beam successively alternately with reflective members. This practice utilizes a rotatable disc assembly comprised of a plurality of discs mounted in spaced relationship along the assembly rotational axis. Each disc is provided about its periphery with a plurality of flat reflective facets arranged at an orthogonal attitude to the assembly rotational axis and mutually spaced by light transmissive portions. The discs are of increasing diameter and misaligned such that each reflective facet of a given disc is aligned with light transmissive portions of the remaining discs. In this manner, rotation of the disc assembly with its rotational axis angled to the path of the laser beam results in successive alternate issuance of the beam from the facets of the different discs. With this practice, spacing the discs may be varied to meet particular perforation pattern spacing requirements.
In another known laser perforating practice employing a disc assembly, successive discs are arranged along the assembly rotational axis in abutting relationship and the discs are provided with reflective facets mutually spaced by light transmissive portions. In this case, the discs are of equal diameter and the facets of the forward disc are at an orthogonal attitude relative to the assembly axis, while those of the rearward disc are at a non-orthogonal attitude relative thereto. Disposition of the rotating assembly angled to the laser beam, again results in successive alternate issuance of the beam from the reflective facets of the different discs.
While the above-discussed laser perforating systems utilizing rotatable disc assemblies are advantageous over prior laser systems from the standpoint of speed of operation and maximum utilization of the laser energy, alternative systems which enable more suitable physical arrangement of the system components and attendant ease of manufacture would be desirable.
It is therefore a broad object of the present invention to provide a laser beam perforating system having features promotive of more suitable physical disposition of system components.